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pH & Hair

Published on 21st September 2005

Hair is made up mainly of proteins and is pretty strong stuff. However, chemical processes can weaken your hair and cause it to break. In this article I’ll explain how the pH of hair products can affect your hair’s condition and how you can avoid unnecessary damage.

The structure of the hair is made of two main parts. The outer layer, called the cuticle consists of overlapping scales which protect the cortex underneath. When your hair becomes damaged the scales of the cuticle can stand out or break off, exposing the cortex and making your hair feel dryer and harder to brush.

The cortex which is in the inner region of the hair is made of a a string of proteins and gives the hair it’s strength and elasticity. This is why damaged hair does not return to shape or even snaps when stretched. The cortex is where menalin (which denotes your natural hair colour) can be found. For this reason most hair colours will need to penetrate to the cortex in order to change your hair colour.

You can measure the pH of anything that is water soluable. The pH indicates how acid or alkaline a substance is. The scale ranges from 0 to 14 with 0 being a very strong acid and 14 being a very strong alkali (aka a base). Both strong acids and alkalis should be avoided as they will burn skin.

Water has a pH of around 7, as does Peroxide and most shampoos. Lemon Juice and Vinegar, both acids, have a pH of around 2 or 3 and baking soda, an alkali, has a pH of around 8 or 9.

Diagram: Cross section of a hair

Hair Colours are Usually Alkaline

Most permanent hair colours are alkaline. When an alkaline substance is applied to hair it opens up the cuticle. With hair colour this allows the mixture to penetrate to the cortex where it can react with the hair’s pigment molecules to produce a colour change. Permanent colours have a pH of around 7-8. With bleach the colour molecules are oxidised, producing the lightening effect. Bleach usually has a pH of around 8 or 9 and if used too often or mixed too strong it will cause the scales in the cuticle layer to break off which causes permanent damage. The layers in the cuticle will no longer lie flat and will stick outward causing hair to snag and tangle. When the scales do not lie flat or when some have broken off the hair is no longer water proof and the cortex is exposed to washing and envirnomental factors. This will cause it to dry out and loose elasticity leaving the hair prone to breakage.

However, you can avoid most of this damage if you only bleach your regrowth each time and do not allow the bleach to overlap onto already bleached hair. Since peroxide has a pH of 7 all the alkalinity comes from the powder. If in doubt mix your bleach to a thinner consistancy with more peroxide and avoid lumps of powder which can cause breakage. If you use a lot of powder the bleach is going to have a high pH which causing damage to the hair.

Acidic Hair Products

Most hair products don’t contain strong acids other than some perming solutions. Conditioner has a slightly acid pH. Mild acid has a an opposite effect to alkalis and flattens the cuticle making your hair easier to comb and look shinier. Many people believe that rinsing hair with vinegar after dyeing helps the longevity of direct dyes such as Manic Panic or Special Effects. This is probably because it closes the cuticle helping the colour stay in the cortex for longer.

Using the pH to your Advantage

So, we know that an alkali will open up the cuticle and an acid will flatten it, so how can we use this to get better hair colour? Let’s assume your hair is already bleached and you’re applying a new shade of colour using something like Directions or Special Effects. If you can get the colour deep into the cortex it will take a longer time to rinse out (these dyes deposit colour molecules into the cortex and fading occurs as the molecules are rinsed out of the cortex). First wash your hair. Hair is coated in a layer of oil to help keep your hair in good condition. This can act as a barrier to direct hair colours like those mentioned above. Now the hair is all clean we can use an alkali to open up the cuticle. A small amount of baking soda disolved in warm water will be adequit. You only need about 1 teaspoon in a pint of water. Keep away from your eyes and allow the mixture to rinse through your hair. Now blow dry the hair until it’s damp. Heat will also help open the cuticle. The hair is now ready to dye. Apply the dye to your hair and leave for 30-40 minutes. Rinse in cold water. Rinse again in a mixture of water and a few tablespoons of vinegar or lemon juice (again, keep away from eyes). Condition your hair leaving the conditioner on for as long as possible and then rinse in cold water. Your hair should now be shiny and will have the best chance of keeping the colour.

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  • Dilute heavily strong acids or alkalines before using them